The Jade Double D is notable for being an intelligent floppy disk controller. The onboard Western Digital FD1791 FDC chip is controlled by a Z80 processor. The CPU communicates with the DD through a 1kB window.
Although the card includes a processor and 2k of RAM it has no ROM. Instead, code must be injected by the CPU card. The code is embedded in the CPU boot ROM.
The boot code assumes that the window address must be set to F400. The jumpers were already correctly set.
This card supports 5.25″ drives on a 34 pin interface or 8″ drives on the 50 pin interface. Eventually i will use 8″ drives with this machine, but in the short term i just wanted to use a couple of goteks (with Flashfloppy).
The images that i wanted to use are from 8″ disks. These work fine in the gotek but because the gotek uses the 34 pin interface there were a couple of residual issues. There are a some signals expected by the boot ROM and the CP/M BIOS for the 8″ drives that are not on the 34 pin interface.
The first is the RDY signal which is supported by Flashfloppy on pin 34. This requires a link on the DD from pin 34 of the 34 pin interface to pin 22 of the 50 pin interface.
The second is that an 8″ drive can detect whether a disk is single or double-sided – the index hole is in a different location. For this, i added a switch to assert or negate the SIDES signal depending on which image i had loaded. I later copied all of the single sided disk images to double-sided disk images to make things a little simpler.
This card had a couple of hardware issues. The first was two shorted tantalums. The second was that, for whatever reason, two sockets had been butchered, and the chips soldered to the socket pins.
I replaced the sockets and devices.